Current mobile communication is more and more tending to provide multimedia service with high rate transmission to users.
FIG. 1 shows a system architecture of System Architecture Evolution (SAE).
As shown in FIG. 1, a user equipment (UE) 101 is a terminal device for receiving data. Evolved Universal Terrestrial Radio Access Network (E-UTRAN) 102 is a wireless access network, comprising a macro base station (eNodeB/NodeB) which may provide the UE an interface for accessing the wireless network. A mobility management entity (MME) 103 is responsible for managing mobility context, session context and security information of the UE. A serving gateway (SGW) 104 mainly provides the user-plane functions. The MME 103 and the SGW 104 may be located in the same physical entity. A packet data network gateway (PGW) 105 is responsible for functions, such as charging, monitoring, and may also be located in the same physical entity with the SGW 104. A policy and charging rules function entity (PCRF) 106 provides policy and charging rules of quality of service (QoS). A serving General Packet Radio Service (GPRS) support node (SGSN) 108 is a network node device providing routing for data transmission in Universal Mobile Telecommunications System (UMTS). A home subscriber server (HSS) 109 is a home subsystem of the UE, responsible for protecting information of the UE, including current location of the UE, an address of a serving node, security information of the UE, packet data context of the UE, etc.
The 3rd Generation Partnership Project (3GPP) has proposed requirements of small cell enhancement in release 12 (Rel-12). Target scenarios of the small cell enhancement include scenarios with macro cell coverage and without macro cell coverage, indoor and outdoor, ideal and non-ideal backhaul enhancement, as shown in FIG. 2.
In the case with macro cell coverage, it has been proposed to apply a technique of carrier aggregation at different base stations. A macro cell and a small cell may work in different bands. There are two kinds of architectures that apply the technique of carrier aggregation at different base stations, i.e., one based on Radio Access Network (RAN) split, and the other based on Core Network (CN) split, for the user-plane data. The architecture based on CN split means that for a bearer established on a pico cell, the user-plane data is directly sent by the CN SGW to the pico cell, but not forwarded by the macro cell.
In the architectures of small cells, the UE may simultaneously transmit and receive data to and from two base stations, named as dual-connectivity, in which only one base station is responsible for sending a Radio Resource Control (RRC) message to the UE, and interconnect with the CN control-plane entity MME, such base station named as MeNB, and the other named as SeNB. One cell in the MeNB for the UE is a primary cell (Pcell) of the UE, through which a RRC message is sent to the UE, and other cells are secondary cells (Scells). One cell among the Scells of the SeNB is a primary Scell of the SeNB (pScell), providing functions of the pScell. There is a physical uplink control channel in the pScell, but none in other Scells. A cell group of the MeNB is named as MCG, and a cell group of the SeNB is named as SCG. Configurations of SCG at the UE side are performed by the SeNB, which is sent from the MeNB to the UE via a RRC container. The MeNB does not parse the RRC container, or parse but not modify the configurations in the RRC container.
When a UE moves, or the channel quality changes, the MeNB can determine to handover the Scell to a new base station, which becomes the new SeNB, called as a SeNB handover, or the MeNB can determine to handover the Pcell to a new base station, which becomes the target MeNB, called as a MeNB handover. During the MeNB handover process, an existing method is to switch all the bearers to the target MeNB, of which the disadvantages are frequent reconfiguration of the bearers, and lack of efficient utilization of the dual connectivity to improve the system throughput and transmission rate of the UE. During the SeNB handover process, according to an existing method, the secondary bearers are established at a new SeNB, and the new SeNB configures the bearer at the UE side. After the bearer establishment is successful, the MeNB sends the bearer release to the source SeNB. It is possible for the source SeNB to configure the bearers at the UE side according to existing methods, so it may occur that the newly established bearers at the UE side would be released. Therefore, the present application relates to the method for the MeNB handover, in which the target MeNB selects the source SeNB as the target SeNB, and further relates to the method for the SeNB handover, in which the MeNB handovers a SeNB to another base station.
In accordance with another aspect of the present disclosure, an apparatus for supporting a user equipment (UE) mobility in a small cell system is provided. The apparatus is configured to perform the method of one of claims 1 to 14.
Therefore, a need exists for a method and an apparatus for UE mobility in a small cell system.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.